Electrolytic apparatus



March 12, 1957 A. H. JOHNSTON 2,785,121

ELECTROLYTIC APPARATUS Filed April 15, 1954 s Sheets-Sheet 1 IN V ENTOR.

Elan .6: .falmsfon/ BY RMvIW March 12, 1957 A. H. JOHNSTON ELECTROLYTICAPPARATUS Filed April 16, 1954 5 Shetg-Sheet a Mm s. MM,

March 12, 1957 A. H. JOHNSTON 2,785,121 I ELECTROLYTIC APPARATUS FiledApril 15, 1954 s Sheets-Sheet 4 0 f'gte 72 4a 'IIIIII'IIIIIIIIIIIIIIII.

IN VEN TOR.

/Ila .falmsian/ aria/ENE) March 12, 1957 Filed April 16, 1954 A. H.JOHNSTON ELECTROLYTIC APPARATUS 'IIIIIIIIIA 5 Sheets-Sheet 5 INVENTOR.

Am/v H Jam 570w (imam l 2,785,121 1 Patented Mar. 1957 ELECTRGLYTICAPPARATU Alan H. Johnston, Arvida, Quebec, Canada, assignor to AluminiumLaboratories Limited, Montreal, Quebec, Canada, a corporation of CanadaApplication April 16, 1954, Serial No. 423,73a

11 Claims. (Cl. 294-247 This invention relates to apparatus forelectrolysis of molten baths and more particularly to apparatus forelectrolytic production of magnesium at the cathode of a fused bath,wherein a gaseous product such as chlorine is released at the anode.

A common method for so producing the metal involves passing an electriccurrent through a bath that contains magnesium in halide form, themolten magnesium, which is lighter than the fused salts, being thencollected as it rises from the cathode. The gaseous product ofelectrolysis, which is chlorine in the presently preferred type ofoperation using magnesium chloride, is collected separately above theanode, it being usually important to prevent contact between theliberated metal and the chlorine gas, since chlorine readily reacts withmolten magnesium to form magnesium chloride. Indeed present experienceis that the greatest over-all eificiency is to be expected inarrangements where there is a minimum of reconversion of magnesium tochloride form, if the cell is also at least reasonably economical inother respects and is satisfactorily convenient to operate and maintain.

A primary object of the present invention is therefore to aiford new andimproved apparatus of the character and for the purposes describedabove, especially to enable the electrolytic production of magnesium inan eflicient, continuous manner and in relatively large quantities,While at the same time facilitating various necessary or incidentaloperations which contribute to economy and efiiciency in the process.

A presently preferred type of bath comprises magnesium chloride, usuallyin a somewhat minor proportion, together with other chlorides such assodium and calcium chlorides and perhaps a very small amount of afluoride, e. g. calcium fluoride, the materials other than the magnesiumsalt serving cooperative functions of increasing the fluidity of thebath, improving its conductivity and otherwise promoting the desiredelectrolytic action, all as will be readily understod. The bath i keptcompletely molten, conveniently by the heat of the electrolytic process.Not only is it important to keep the chlorine away from the liberatedmetal, but it is likewise desirable to prevent exposure of the cathodeto chlorine at regions above the bath, since the chlorine will attackthe cathode, which is usually made of iron or steel.

Various cell arrangements have been used or proposed to achieve theseand other operating requirements, but in general such apparatus has beenless than entirely satisfactory. For instance, because of structuraldifliculties, prior cells have often been of rather small or moderatesize, so that a great number of units must he provided and separatelyattended in order to obtain a large output of the metal. This limitationof size has been especially serious Where the cell vessels have beenlined with refractor materials rather than composed almost entirely ofiron or steel, but in no such case has there been provision ofeffective, practical, large scale apparatus, for example wherein themagnesium metal might be collected at one place from many cathodesrather than at a plurality of places or in a multiplicity of separatecells. In some cell constructions provision has been made forprogressive feeding of the graphite anode rods, and While such operationmay be useful where the anodes are attacked because of moistureunavoidably introduced with magnesium chloride that has been produced bya wet process,'the stated cells are at the same time poorly adapted forcollecting chlorine which is free of air or other contamination; yet itpure chlorine can be recovered, it can be employed for preparinganhydrous magnesium chloride by a dry process, and use of anhydroussalts in the electrolytic bath will avoid attack on the anodes.

For example, where magnesia is obtained in a dry state, as by'appropriate separation from ore in which magnesium compounds occur (e.g. the calcination of magnesite), an effective process for makingessentially anhydrous magnesium chloride comprises treatment of themagnesia With chlorine gas in the presence of carbon, e. g. in asuitably heated furnace. If the chlorine derived from the electrolyticcell is to be economically employed for this high temperature method ofproducing magnesium chloride, it should be essentially pure, i. e. freeof air or the like; hence the collection of uncontaminated chlorine isanother desideratum of the cell itself.

Another problem which arises with magnesium cells, is the difliculty ofsludge removal. During the operation of these electrolytic procedures, aconsiderable amount of sludge continuously accumulates at the bottom ofthe fused bath. Among other things, the sludge contains iron which isderived from the magnesium or other salts, and

lthough the iron does not seriously contaminate the molten magnesiumthat floats up, the accumulating sludge may not tend to clog the cellbut will increasingly reduce the electrical efficiency, becauseits ironcontent provides a non-useful, low resistance path through aconsiderable region of the bath. Accordingly it is desirable to scrapeor scoop the sludge from the bottom of the cell at frequent intervals,yet in a number of prior structures such work could only be accomplishedby interrupting the electrical operation and removing some or all of theelectrodes.

While in prior cells an effort has usually' been made with screening orshielding structures to separate the magnesium-collecting andchlorine-releasing regions at and above the bath surface, thesearrangements, in cells of even moderately large capacity, have generallyrequired delicate or ditficultly supported shapes of refractory materialor the like. Such structures, however, are apt to need frequent repairor reconstruction, in that any chemical attack or deterioration by heatwill seriously weaken or damage the special and relatively delicaterefractory parts after a short time, especially Where the parts have tocooperate in the support of the anode or cathode.

Accordingly, a further object of the invention is to provide improvedand efiicient apparatus for electrolysis of fused baths, wherein thevarious problems and difficulties described above are substantiallyovercome. A particular object is to afford a rugged, large capacity cellfor the production of magnesium, the cell vessel being of refractoryconstruction and having an unusually long life, against need forreplacement or repair of refractory elements. Another special object isto provide an improved cell wherein molten magnesium may be collected,in a common region, from a multiplicity of separate cathodes, andwherein the evolved chlorine can be collected in a pure state, from acorresponding plurality of anodes and without attack on the cathodes orsignificant-reconversion of the liberated magnesium metal.

To these and other ends, including the provision of a novel cell adaptedfor ready practical achievement of the functions explained above,certain presently preferred embodiments of the invention are shown inthe accompanying drawings and described below, by way of example toillustrate the features and principles of improvement.

Referring to the drawings:

Fig. 1 is a plan view of a multiple-electrode. cell embodying theinvention, showing certain parts successively broken away and a portionin horizontal section;

Fig. 2 is a vertical section on line 22 of Fig. 1;

Fig. 3 is an enlarged vertical section of an anode mounting structure;

Fig. 4 is a vertical section on line 44 of Fig. 2;

Fig. 5 is a side elevation of a double cathode structure embodied inFigs. 1 and 4;

Fig. 6 is an end elevation of the cathode assembly of Fig. 5, from theleft-hand end;

Fig. 7 is a horizontal View on line 7-7 of Fig. 5;

Fig. 8 .is a plan view of a part of a cell cover structure, such asshown in Figs. 1 and 4, with certain supplemental means;

Fig. 9 is a section on line 9-9 of Fig.8;

Fig. 10 is a vertical section on line 1010 of Fig. 2, on reduced scale;7

Fig. 11 is a transverse vertical section similar to Fig. 2 and showing amodified structure; 7

Fig. 12 is a fragmentary view in vertical section, partly on line 12al2aand partly on line 1212-1212 of Fig. 11; and

Fig. 13 is a horizontal section of the cell of Fig. 11, on line 13-l3 ofFig. 12, on reduced scale.

Referring particularly to Figs. 1, 2, 4 and 10, the illustrated cell,which is especially designed for production of magnesium by electrolysisof a fused bath containing magnesium chloride, is enclosed in a box-likesteel shell 20, externally reinforced and supported by appropriatestructural steel work adjacent the walls as indicated at 21 and asprovided by the supporting beams 22 beneath the bottom 24 of the shell.Inside the steel shell there is a horizontally elongated, rectangularmain chamber generally designated 25 and a supplemental ormetalcollecting chamber 27 extending parallel to the main chamber alongone of the longer sides of the latter, specifically, the inner wallsystem of the cell, defining the stated chambers, is composed ofrefractory material, arranged in the nature of a lining of the steelshell but in fact essentially self-supporting like a massive structureof masonry. Thus the entire cell, constituting the two chambers and 27,has a rear wall 28, a front wall 29, end walls 30 and 31, a partition orcurtain wall 32 separating the two chambers, and a floor 33.

The main chamber 25 is conveniently higher at the top than the otherchamber, by reason of'upwardly extending refractory structures 34, 35,36 and 37, respectively rising from the walls 28, 32, 3t and 31. Thechamber 25 is closed by a refractory lined cover generally designated40, which rests on the upper wall extensions just described and whichhas a detail construction as explained below. The supplemental chamber27 may also, if desired, have a relatively light sheet metal cover 41(aluminum or aluminum-faced) which may have a vent stack 42 and whichcan be arranged for ready removal to afiord access to the chamber 27.

The electrodes are disposed in the main chamber 25 and are convenientlylarge and generally rectangular members disposed in an upright positionin a spaced parallel array, with the anodes and cathodes alternating.Thus the anodes may consist of heavy slab-like plates or blocks 44 ofgraphite, suspended from the cover 40, while the cathodes generallydesignated 45 are essentially steel or'iron plates, likewise of upright,rectangular, shape, arranged in an interleaved, spaced relation to theanodes. Specifically, in the cell shown, there are so-called singlecathodes at the ends of the array (see Fig. 4), while between eachsuccessive pair of anodes there are two cathodes 45, constituting adouble cathode assembly, for disposition efficiently close to theadjacent anodes while permitting appropriate spacing of the variouselectrode supporting and connecting instrumentalities in the cell wallor cover. As shown, the cathodes are wholly supported by metal plates 47which extend through the rear wall 28 of the main chamber 25, so thatall portions of the cathodes are kept below the fused bath surfaceapproximately indicated by the dot-and-dash line 48 in Figs. 2 and 4. I

Trough assemblies generally designated 49 are mounted at the top edgesof the cathode plates 45 and are arranged to slopeslightly upward fromthe end of the cathodes near the rear wall 28, toward and through thepartition wall 32, the forward ends 5% of the troughs thus projectinginto the supplemental chamber 27 through corresponding doors 52 in thecurtain wall 32, such doorways being particularly shown in Fig. 10(which for clarity shows only one cathode assembly) and also indot-and-dash line in Fig. 4. Although in some cases other types ofopenings may be employed, or in some special instances a partitionarrangement can be used which is in effect no more than an upper curtainthat separate the two chambers at localities above the electrolyte level48 (and a small distance beneath) and leaves the side of chamber 25essentially entirely open below, the illustrated partition wall, withdoorways as shown, represents a specific and important feature ofimprovement, afiording the desired results and at the same timeembodying a relatively simple, rugged construction of self-supportingnature. It will be understood that in any event the two chamberscommunicate beneath the fused clectrolye, e. g. through the doorways 52,the molten salt level thus rising in the chamber 27 to such point asindicated at 54 in Fig. 2.

As will now be understood, metallic magnesium released by electrolyticaction at the cathodes 45 rises along the sides of the latter,collecting under the trough assemblies 49 so as to travel along theirsloping undersides to the chamber 27. There the molten metal rises fromthe ends 54 of the troughs, to collect as a supernatant layer 55 (Fig.2) above the surface 54 of the molten salt. The other principal productof electrolytic action, viz. chlorine gas released at the anodes 44,rises above the electrolyte level 3 in the chamber 25 and may dischargethrough an appropriate pipe 57 at an upper part of one of the chamberwalls (e. g. the upper wall extension 36 as seen in Figs. 1 and 4), thepipe 57 leading to a suitable locality (not shown) for use or otherdisposition of the essentially uncontaminated chlorine.

The described cell arrangement thus provides a relatively large, single,main chamber 25 wherein a plurality of anodes and cathodes ofconsiderable size are supported in parallel alternating arrangement, forlarge production of magnesium. At the same time the troughs 4? and thepartition wall 32 with its doorways 532 afford collection of theproduced metal'in a single locality, viz. at the surface of the moltenbath in the supplemental chamber 27, the metal being easily skimmed fromthe surface layer 55 at desired times (or drawn from a collecting well,not shown, at one end of the chamber). The partition wall 32 likewisecompletes the enclosure of the chlorine-collecting compartment, for thedescribed separate removalyof pure chlorine.

.Referring now also to Figs. 5, 6 and 7, one form of a suitablestructure for each of the double cathode assemblies comprises a pair ofmetal plates 45, e. g. of iron or mild steel, which may be of anydesired dimensions (in one practical example, each was 2 /2 feet by 3feet) and which are reinforced on their adjacent faces by smaller,overlappin plates 6% arranged in stepped relation, the reinforced platestructures being held and spaced apart by studs 61 and being securedalong one vertical edge to a long, upright mounting block 62. The block62 is carried at the end of the supporting plate 47, and if 'desired maybe formed integrally therewith. As shown,

the block 62 is disposed between the cathode plate assemblies at the endlocality of each where all of the reinforcing plates are secured to it,so that the entire double cathode structure is securely and rigidly heldon the block and thus at the end of the mounting plate 47.

The plates 47 (Figs. 1 and 2) traverse the rear refractory wall 28 ofthe main chamber, through rectangular steel sleeves 63 that project fromthe housing 24, the plates being sealed in the sleeves by suitable meanssuch as a thick layer of refractory cement 64, which also serves anelectrical insulating function. Bus connections generally designated 65are shown at the outer ends of the cathode support plates 47, and mayextend, in a conventional manner, to the negative side of an appropriatesource of direct current, not shown.

The trough assemblies 49 are heavy sheet metal structures comprising aninverted trough extending along and above the top of each cathode plate45, and having downwardly and outwardly flaring skirts 67 which projectover the outer sides of the plates, and similar, somewhat deeper skirts68 above the inner surfaces. At the end adjacent the supporting plate47, the long troughs 4 are joined by a like, transverse trough 69,similarly skirted and communicating with both of the others so as toform a long U-shaped trough structure which is thus adapted to collectany molten metallic magnesium rising from all faces of the cathodedevices 45, 69, and both faces of the supporting block 62. The troughassembly is supported on the cathode plates by suitable bracketsfastened at the upper edge of the latter.

At its opposite end from the support block 62, each trough 49 narrows,by virtue of funnel sections 71, to an inverted U-shaped section 72which terminates in the upwardly flaring mouth 50. As shown in Figs. 1and 2, the sections 72 project through the doors 52 of the partitionwall 32 so that the molten metal leaving the trough months 50 rises tothe surface 55 in the supplemental chamber 27. As also noted, thetroughs, with their extensions 72, have a gradual upward slope from thetransverse section 69 to the months 50, to promote the desired flow ofthe metal. While a small amount of magnesium may be electrolyticallyreleased at the upper surfaces of the iron or steel trough assemblies,and thus lost (in a temporary sense) by reconversion to magnesiumchloride upon rising to the atmosphere of chlorine above the bath in themain chamber 25, the amount of metal involved and the current consumedin releasing it are found to be minor and thus to represent unimportantimpairment of the over-all cell efiiciency, which is exceptionally high.If desired, these upper surfaces of the troughs may be faced withelectrically insulating materials or alternatively the troughs maythemselves be constructed of non-conducting refractory materialssuitably attached to the cathodes. For effective avoidance of attack orcorrosion, the cathode assemblies and troughs, all as supported by theplates 47 through a wall rather than the top of the cell, are entirelysubmerged in the bath at all times.

It will be understood that the cathode plates 45 are preferably somounted as to afford the optimum value of anode to cathode distance forthe actual dimensions, proportions and capacity of the particular cellor type of cell which is to be constructed in a given case. Such optimumvalue of electrode spacing (and consequently the value of voltage to beapplied to the cell) should ordinarily be selected to yield the mostefficient utilization of electrical energy in the apparatus; oneadvantage of the present invention is that the determination of suchspacing can be readily facilitated, if necessary, by simple tests withadjustably mounted cathodes or adjustable cathode extensions, in asuitable prototype cell made as herein described and having the chosensize and other characteristics. Indeed it will be further understoodthat other arrangements or surface shapes of the cathode plates can beused, the chief requirement being to have lid an upright cathodeassembly of generally extended shape disposed beneath the skirt 67 ofthe trough and providing relatively large, more or less upright surfacestructure closely facing the nearest anode slab.

The single cathode assemblies at the ends of the cell (Figs. 1 and 4),which each face an anode 44 only at one side, consist of a single,reinforced cathode plate 45, having a single trough assembly 49 with alike projecting portion 72 and a mouth 5!) opening in the supplementalchamber. The supporting assembly for each single cathode likewise (asshown) resembles the structure of block 62 and plate 47 for the doubleassemblies, but with the block projecting from only one side of thesupport plate toward the single cathode 45. As will also now beapparent,-the described mounting of both double and single cathodesthrough the wall 28 wholly supports all of them in spaced relation abovethe refractory floor 33, keeping them clear of any accumulating sludgeand indeed facilitating the removal of the sludge itself. Wherenecessary or desirable for reasons of added mechanical strength orrigidity it is of course possible to provide additional support for thecathodes in the form of small refractory blocks or piers extending fromthe bottom of the cell to the bottom of the cathode at locations wheresuch supports will not interfere with removal of the sludge.

The anodes 44 are shown carried by the cover assembly 40, from whichthey project downwardly into the bath. Although in some cases the anodescan instead be mounted to enter the cell sidewise through the rear wall28 (between the cathodes) with equivalent electrolytic function and someof the other advantages (including separate removal of chlorine andmagnesium), the top-entering anode mounting is particularly convenient,not only by reason of the removable nature of the cover assembly asdescribed below, but also for avoidance of undue heating efiects,electrical leakage, and consequent deterioration as may sometimes occur(unless there is special cooling and insulation) in a wall through whichboth anodes and cathodes pass in close spacing.

The top assembly 40 comprises a metal, e. g. steel, shell having a frameof four upright side walls 78 and a transverse sheet 79 horizontallyspanning the interior of the rectangular frame, so that the shellconstitutes an inverted tray or pan, which is filled at its undersidewith a thick body of refractory material 80. The anodes 44 projectthrough rectangular slots 81 in the refractory body and the cover plate79. An upright rectangular sleeve 82 is disposed above each slot 81 toreceive and support the corresponding anode 44, and is carried by ahorizontal flange 83 at its lower end, appropriately bolted to the plate79 (Pig. 3). A coil of pipe 85 surrounds each sleeve 82, for circulationof water or other coolant fluid to remove heat from the end portion ofthe anode and thus prolong the life of the assembled structure.

At their upper ends, the anodes 44 are secured between clampedassemblies 86, 87, which secure the lower ends of the bus bars 88 thatextend to the positive side of the current supply (not shown), Althoughthe anodes are shown as single slabs of graphite (or other carbon orsimiiarly appropriate composition), it will be understood that each canbe composed of a row of edgewise abutting vertical bars, the clampingmeans 86, 87 then serving to hold the bars in assembled relation so asto have the configuration of a single slab.

The actual support of each anode 44 is effected by the sleeve or bracketstructure 82, in which the anode is suspended in sealed relation byappropriate means, such as a layer of magnesium 29 poured in place. Thesleeves 82 are appropriately insulated (electrically) from the coverplate 79 by suitable gaskets 91 and by washer assemblies 2 surroundingthe shanks of the bolt 93 by which the flanges 83 are secured to theplate 79. An open top box 95 is also carried at the upper end of eachelement 82, with its bottom wall closely fitting the anode.

After assembly, box 95 is filled with pitch or similarly suitablematerial (not shown) for effective seal of the upper ends of the anodes,i. e. so that the latter and the clamping parts 86, 37 are submerged inthe sealing compound. As in the case of the cathodes additionalmechanical support, though ordinarily unnecessary, may be provided inthe form of small piers or blocks, supporting the anodes on the cellfloor at one or more points.

A convenient feature of the described apparatus is that in first settingit up, and likewise at times when replacement of the anodes or otherservicing may be required, the cover 40 can be assembled upside down,separately from the cell. To that end, the frame 7879 is appropriatelysupported in an inverted position with its normally lower cavity facingupward. The refractory material 89 is installed, and the sleeve brackets82. having already been secured in place, in registration with theopenings 81, the anodes are inserted and the magnesium metal 90 pouredto hold them in sealed relation, the bottom of the box 95 in each caseserving to retain the poured metal. The cover, thus holding the severalanodes, is then hoisted and turned over and lowered into place at thetop of the cell. The sides 73 of the cover shell depend skirt-like belowthe refractory body '84), so as to seat in a corresponding groove 97which runs all around the upper edge of the refractory walls of the maincell chamber 25, i. e. in the top surface of the extensions 34, 35, 35and 37 (Figs. 2 and 4). The groove 97, which is somewhat wider than thethickness of the cover sides 78 (that are now resting on the bottom ofthe groove), is then filled with pitch, chlorine-resistant cement, orother sealing material, so that the entire cover assembly is effectivelyyet removably sealed in place. Finally, the clamps 86, 87 and bus bars88 are attached and the boxes 95 filled with pitch or the like asexplained above. 7 While the entire filling 8b of the cover can besimply a body of plastic refractory, e. g. a cement poured and set inplace (preferably with a slight clearance at the openings 81, around theanodes), some provision may be employed for keying the material, e. g.as detailed in Figs. 8 and 9. Thus the lower face of the transverseplate 79 may carry, at suitably distributed localities, pairs ofdownwardly depending, flanged metal brackets $9, each arranged to engageand retain the correspondingly grooved side walls of specially shapedrefractory keying blocks 1%, which have downwardly and outwardly flaringsides and which thus facilitate the retention of the refractory cement80 between them. A layer of insulation 102 may also be disposed betweena major part of the refractory parts 80, 1%, and the cover plate 79,similar to the layer of like insulation 103 which immediately abuts theinner face of the cell casing 20.

While for simplicity in Figs. 1, 2 and 4, all of the main walls andfloor of the cell are shown as if made of poured refractory material, itwill be understood that these parts are conveniently and indeedpreferably built of refractory brick, block or the like, as seen in Fig.10, for superior structural strength and durability. Thus all of theouter, vertical walls of the cell, as likewise the floor, are built ofrefractory brick work, and also the parts of the partition wall 32between the doorways 52, e. g. as indicated at 104 in Fig. 10. The upperpart of the partition wall is similarly. made of brick or blockstructure, in the general manner of such masonry; for instance, theopenings 52 are spanned by suitably keyed or tapered blocks 165, theremainder of this course being completed with other blocks tee ofopposite taper. Finally, the uppermost wall portion 35 may compriseseveral courses of shnple, refractory brick work. Thus the entirerefractory structure of the cell is ruggedly built of bricks or blocks,in an essentially self-supporting manner, and is such as to be capableof continuous use for very long periods of time without need for repairor reconstruction.

As stated, normal operation of the cell with a fused halide bathcontaining magnesium chloride tends to produce a certain amount ofsludge which settles to the bottom, particularly in the main chamber 25.By virtue of the supplemental chamber 27 (easily accessible upon removalof its cover 41), suitable long-handled rakes or scrapers can beinserted downwardly into the body of molten salt and through one oranother of the doors 52, and can then be used to rake the accumulatedsludge along the bottom 33 from the vicinity of the rear wall 23 to andthrough the doors. Thus brought into the supplemental chamber 27, thesludge may be scooped up and out of the bath with the same or otherlonghanded instruments.

it will be noted that the spacing and disposition of the double andsingle cathodes is such as to facilitate sludge removal, the spacingstuds 61 of the double cathodes being located only at localities above adiagonal line across the plates 45 (Pig. 5), to allow the handle of thecollecting instrument to pass between the plates. If desired, raisedsections or curbs 108, having downwardly sloping faces 1% along theirupper sides, may be built up from the floor beneath the anodes 44 atlocalities between the doorways 52. These curbs, above which the anodeshang in spaced relation, serve to channel the sludge into the localitiesbeneath the cathodes, for most effective removal as described above. Itwill now be seen that in the present cell, sludge (which may impair theelectrical efficiency by reason of its iron content) can be easilycleared out as often as desired, e. g. every few days or oftener.

The described cell is adapted for operation with molten salt baths ofvarious compositions, one satisfactory example being as describedqualitatively hereinabove and containing, for instance, about 15%magnesium chloride, 30% calcium chloride, sodium chloride and a smallamount of calcium fluoride, i. e. 5% or less. The operating temperaturein the 700 C. or so; for example, excellent results have been obtainedwhen it is maintained at 720 plus or minus 30", the entire heat (duringcontinuous operation) being obtained from the electrolytic actionitself.

From time to time a so-called bleeding operation may be required with abath of the above type, when the calcium chloride content becomes toohigh by reason of additions of such salt as an impurity in the magnesiumchloride. To perform such operation a siphon tube is simply inserted inthe supplemental chamber 27 to siphon off a suitable amount of themolten electrolyte, which is then replaced with an appropriate mixturecontaining only the other bath ingredients. For instance, the calciumchloride can thus be kept between 25% and 40%, to provide an averagecontent of about 30%. it will be understood that as the magnesiumchloride itself is depleted by the desired electrolytic action producingmagnesium and chlorine, further quantities of this salt are addedthrough the chamber 27, if desired in molten form. The operation of thecell has been essentially explained throughout the foregoingdescription. At the outset, assuming that the apparatus is fullyassembled, with the cover and anodes in place, the cell is filled withthe salt mixture, conveniently in molten form, and suitable currentsupply is then initiated to the bus bar 65, 38. Electrolytic actionproceeds efiiciently, causing accumulation of essentially pure chlorinegas in the upper part of the main chamber 25, from which it may becontinuously withdrawn through the pipe 57, as for effective use in thedry process of making magnesium chloride. At the same time, metallicmagnesium of hi h purity, is continuously collected under the troughs 49and delivered to the supplemental chamber 27, where it may be removed asdescribed above. The entire operation may run continuously for anindefinite period of time,'usual1y requiring only regular replacement ofmagnesium chloride and other supplemental steps as explained.

As will be appreciated, any of various refractory materials can be usedfor the walls, floor and roof of the cell,

cell is usually of the order of V such as good: quality fire clay brick,or other aluminum lihood of attack, e. g. in the vicinity of theelectrolyte surfaceor at regions of contact with molten magnesiumv Notonly are the described results of efiiciency and convenience achieved bythe cell, but it may have an unusually large capacity, i. e. byemploying a multiplicity of anodes and cathodes (as shown) and withoutrequiring the individual electrode elements to be unduly cumbersome ordiiilcult to support. Indeed the specific number of electrodes shown ismerely illustrative; for example, with the cell chambers longer, stillgreater numbers of anodes and cathodes may be employed if desired. Thesupplemental chamber 27 is preferably relatively narrow, i. e. as shown"in Fig. 2; it should be small enough to keep its portion of the bathmolten (by conduction of heat from the main chamber 25), but largeenough to alford convenient removal of magnesium metal and ready accessto'the main chamber, through the doors, for de-sludging. The

electrolytic action is advantageously restricted, in effect,

' to the main chamber 25 which is fully sealed at all localities abovethe bath surface, to prevent undesirable leakage of chlorine. As alsoexplained, the removable cover structure 48 has various specificadvantages and so supports the anodes that they, like the cathodes, arewholly elevated from'the bottom of the cell, it being difiicult to holdlarge anodes in other ways without resting them on the cell floor orsuitable pedestals.

In Figs. ll, 12 and 13 a modified structure of inverted troughs over thecathodes is illustrated, it being understood that these views representa simplified illustration of the cell in other particulars in that manydetails have been omitted for clarification but may be identical, inuse, with what is shown in the preceding figures. The cell in Figs. ll,12 and 13 embodies the same walls 28, 29, 30, 31 and 32, which togetherwith the floor 33 define the main chamber 25 and the supplementalchamber 27. Thesame array of anodes 44 are provided, suspended from thecover 40, with cathodes between successive anodes, carried by themembers 47 through the rear wall 28. For variety of illustration, thecathodes 45a are shown arranged to slope outwardly at the bottom, i. e.toward the adjacent anodes, with some advantage in efficiency by reasonof a shorter average electrical path between cathode and anode.

The troughs over the cathodes, for conducting molten metal through thedoorways 52 into the supplemental chamber 27, are made of refractorymaterial, and specifically consist of single, monolithic blocks 120, 121which at their ends are embedded in and supported by the rear refractorywall 28, and at their forward ends are disposed within, and as part of,the curtain wall 32, each block being conveniently sufliciently wide sothat the side portions of its bottom rest, at this locality, on upperfaces or shoulders of the refractory brick work 104 constituting theupright supporting portions of the wall 32 between the doorways 52.

As shown, the underside of each of the blocks 120, 121 is hollowed outat 122, 123 respectively to provide an inverted trough-like contourabove the cathodes, the underside of each block and the surface of theinverted troughs 1 22, 123 being arranged to slope slightly upwardfromthe vicinity of the rear wall 28 to the forward ends 'of the blocks,in the side of the w all 32 facing the V chamber 27. As will be seen,the blocks 120 which are By the provision of the inverted troughstructure in the form of these refractory blocks 12%, 121, some improve-'ment of electrical efficiency is obtained, e. g. in that there is nocurrent lost in releasing magnesium metal at the upper surface' of metaltrough structures where such recombine with chlorine.

magnesium cannot be collected and thus simply rises to At the same timethe cathodes 45a and their supports 47 are relieved of mechanical loadof the troughs, the blocks 12%, 21 being very elfec-tively supported bythe heavy refractory walls 32, 28. Since the distance across the cellspanned by these blocks is relatively short (an advantage of the cellbeing that its large capacity is obtained by the arrangement ofsuccessive anodes and cathodes arrayed through the considerably greaterlength of the chamber 25 in the other direction), the blocks can besupported at their ends as shown and yet can be inherently of suflicientstrength so as not to crack orbreak over extended periods of service.

These blocks, of course, may be constructed of conventional refractorymaterial named above, made in the usual fashion of casting or moldingpro-formed bodies of such material. While in the cell of Figs. 11 to 13inclusive the blocks are shown as particularly massive for optimumstrength and thus such that the bath level 48 within the chamber 25, andlikewise the levels 54, 55 in the chamber 27 are intermediate the topand bottom of each block, it is contemplated that shallower blocks maybe employed in some cases such as to be wholly submerged in the bath,with the advantage that there is then less attack on the refactorymaterial such as is particularly greatest at theelectrolyte-to-atrnosphere interface. The function and effect of theinverted troughs over the cathodes constituted by the blocks 120, 121 isexactly as described above rela tive to the troughs 49 in Figs. l to 10,namely in collecting the molten magnesium which rises from the cathodesand in conducting such metal to the supplemental chamber 27, where itfurther rises to the surface for removal.

T his application is a continuation-in-part of my copending applicationSerial No. 274,377, filed March 1, 1952 for Electrolytic Apparatus, nowabandoned.

it is to be understood that the invention is not limited to the specificapparatus herein shown and described, but i may be embodied in otherforms without departure from 'rising and supported from the bottom ofthe cell and dividing the cell into main and collecting chambers, saidpartitioning wall having open regions therein spaced below the top ofthe cell for communication between the chambers, the aforesaid wallstructure including a wall for the main chamber opposite thepartitioning wall, cover means closing the main chamber, means for ex- 7hausting gas from the main chamber above the fused bath, a plurality ofcathodes in parallel array in the main chamber, each cathode beingdisposed crosswise of the main chamber between the partitioning wall andsaid opposite wall and each cathode having substantial extent bothvertically and crosswise of the main chamber, means extending laterallythrough wall structure of the main chamber other than the partitioningwall and spaced below the top of the cell, for support of and electricalconnection to said cathodes, anode means between said cathodes inmutually facing relation therewith, and means providing inverted troughsurfaces over the cathodes, extending'across the main chamber andthrough the partitioning wall, for leading molten metal released at thecathodes into said supplemental chamber, said cathodes being disposedbelow the said trough surfaces, and said cell Wall structure havingupper parts and said partitioning wall having an upper portion, saidparts and portion being above, and being arranged to hold fused bath inboth chambers to a level wholly above said inverted 2.'Appar'atus' asdescribed in claim l,"wherein said main and collecting chambers have arefractory floor that extends across both, and wherein the partitioningwall includes supporting refractory portions extending upward from saidfloor, the open regions of the wall being constituted by doorwaystherein between said supporting portions, said doorways extendingdownward to the floor and providing access from the top of thecollecting chamber through the fused bath to the floor of the mainchamber for removal of sludge from said main chamber floor, saiddoorways extending upward to the localities of the inverted troughsurfaces, and said inverted trough means being arranged to guide themolten metal into the collecting chamber through the doorways at upperportions of the latter.

3. Apparatus for electrolysis of a fused bath to produce at the cathodea metal lighter than the bath, comprising refractory wall structuredefining a fused bathreceiving cell, a self-supporting partitioning wallof refractory material extending from the bottom of the cell andpartitioning the cell into main and collecting chambers, the aforesaidwall structure including a wall for the main chamber opposite thepartitioning wall, cover means closing the main chamber, a plurality ofcathodes in parallel array in the main chamber, each cathode beingdisposed crosswise of the main chamber between the partitioning wall andsaid opposite wall and each cathode having substantial extent bothvertically and crosswise of the main chamber, anode means between saidcathodes in mutually facing relation therewith, said partitioning wallhaving open regions therein spaced below the top of the cell forcommunication between the chambers, said collecting chamber and saidopen regions being cooperatively shaped and arranged to providemechanical access down through the collecting chamber and said openregions to and across the floor of the main chamber, and molten metalcollecting means providing guiding surfaces extending across the mainchamber over the cathodes and opening into the collecting chamber atcalities higher than the cathodes for delivering molten metal from thecathodes into the collecting chamber, said cell wall structure havingupper parts and said partitioning wall having an upper portion, saidparts and portion being above, and being arranged to hold fused bath inboth chambers to a level wholly above said guiding surfaces, cathodes,and open regions, said partitioning wall wholly separating the chambersat its said upper portion.

4. Apparatus as described in claim 3, wherein said main and collectingchambers have a refractory floor that extends across both and whereinthe partitioning wall includes supporting refractory portions extendingupward from said floor, the open regions of the wall being constitutedby doorways therein between said supporting portions, said doorwaysextending downward to the floor and being disposed in registration withthe adjacent ends of the aforesaid cathodes, said apparatus alsoincluding means disposed below said metal guiding'surfaces and extendinglaterally through the aforesaid opposite wall of the main chamber to thecathodes for support and electrical connection thereof.

5. Apparatus for electrolysis of a fused bath to produce at the cathodea metal lighter than the bath, comprising refractory wall structure anda refractory floor defining a cell vessel for receiving the fused bath,a selfsupporting refractory wall extending upward from the floor of thecell vessel and dividing said cell vessel into main and supplementalchambers, mutually spaced cath-' odes and anode means arranged inalternate parallel array in the main chamber and extending transverselythereof relative to the said dividing wall, each cathode havingsubstantial extent both vertically and in a transverse directionrelative to the dividing wall, means extending through wall structure ofsaid main chamber spaced from said dividing wall for supporting saidcathodes above the floor, cover means sealing the top of the mainchamber and comprising refractory material facing said main chamber,means carried by said cover means for suspending said anode means, saiddividing wall having doorways at the ends of the cathodes, extendingdown to the floor and providing access through the supplemental chamberand the fused bath to the floor across the main chamber, and invertedtroughs over the cathodes extending through the doorways for leading theproduced metal from all the cathodes into the supplemental chamber, saiddoorways having their upper ends above the cathodes, said refractorywall. structure having upper parts and said dividing wall having anupper portion, said parts and portion being above, and being arranged tohold fused bath in both chambers to a level wholly above said doorwaysand cathodes and above the paths of metal along the inverted troughs,said dividing wall wholly separating the chambers at its said upperportion.

6. Apparatus as described in claim 5, wherein the cover means comprisesan inverted tray-like shell lined below with refractory material anddisposed on said dividing wall and the portions of said refractory wallstructure which complete the boundary of the main chamber, said anodemeans comprising a plurality'of upright anodes extending through thecover means and supportedwithin the main chamber and above the floorthereof by said suspending means, said suspending means holding saidanodes in sealed relation to the cover means, said cathodes comprisingat least several upright cathode structures interspersed withsaid'anodes to constitute said alternate array, each of said anodes andcathode structures being sustantially perpendicular to said dividingwall and said cathode supporting means comprising metallic supportingmembers traversing the wall of the main chamber opposite thesupplemental chamber, for respectively holding the cathode structures.

7. Apparatus as described in claim 5, wherein the cover means comprisesan inverted tray-like metal shell partially filled with refractorymaterial throughout its under cavity and having depending metal skirtportions around its periphery, said dividing wall consisting ofpreformed refractory shapes laid up in self-supporting relation upon andfrom the floor of the cell, said dividing wall and the portions of saidrefractory wall structure which complete the boundary of the mainchamber having grooves along their upper edges, the aforesaid metalskirt portions of the cover being seated and sealed in said grooves.

8. Apparatus as described in claim 5, wherein said inverted troughscomprise refractory blocks each having a trough-like contour on itsunderside and each supported at its ends respectively in a portion ofthe first-mentioned wall structure of the main chamber opposite thedividing wall, and in the said dividing wall at localities bridging thedoorways.

9. Apparatus as described in claim 5, wherein the said self-supportingdividing wall consists of preformed refractory shapes laid up inself-supporting relation upon and from the floor of the cell vessel,said refractory shapes being mutually disposed to provide the aforesaiddoorways and to constitute the aforesaid upward extent of thedividingwall.

10. Apparatus for electrolytic production of magnesium at the cathode ofa fused bath releasing chlorine gas at the anode, comprising a vesselfor receiving the fused bath, said vessel being internally faced withrefractory material, a plurality of upright cathodes arranged in spaced,parallel array in said vessel, each cathode having substantial extentboth vertically and crosswise of the array, supporting and connectingmeans for said cathodes extending through a side wall of said vessel, aplurality of vertical anodes arranged in spaced parallel array in thevessel, said anodes being interspersed between the cathodes in spacedrelation thereto, said vessel having cover means enclosing it at thetop, means extending through said cover means for support of andconnection 13 to said anodes, said vessel including means for dischargeof chlorine gas collected above the bath, said vessel having anotherside wall opposite the first-mentioned side wall and extendingtransversely of the cathodes, said second side wall consisting ofrefractory material rising and supported from the bottom of the vessel,said vessel including means internally faced with refractory materialand providing a suplemental chamber along the outer side of said secondside wall, said supplemental chamber extending upward from the aforesaidbottom of the vessel, said second side wall including a plurality ofdoorways spaced lengthwise thereof and disposed at a lower part thereofin registration with the adjacent ends of the cathodes, said second sidewall preventing access between the supplemental chamber and the vesselabove the doorways, and said doorways and said supplemental chamberbeing shaped to provide access from the top of the supplemental chamberthrough the fused bath to the bottom of the vessel for mechanicalremoval of sludge from said bottom, and molten magnesium-collectingmeans extending along upper portions of the cathodes and including meansguiding molten magnesium into the supplemental chamber through thedoorways, for delivering said magnesium from all of the cathodes intosaid chamber, said vessel, including its said second side wall and itssaid 25 supplemental chamber means having sufiicient upward extent toreceive fused bath in the vessel and supplemental chamber to a level ineach which is wholly above said doorways, cathodes, andcathode-supporting and connecting means, and above the paths of moltenmagnesium along the collecting means.

11. Apparatus as described in claim 10, wherein the magnesium-collectingmeans for the cathodes consist of a plurality of refractory blocks abovethe cathodes and arranged with the anodes interspersed between saidblocks, each block having an inverted trough contour at its undersideand being supported at its ends respectively in the first-mentioned sidewall of the vessel and in the secondmentioned side wall in bridgingrelation to said doorways.

References Cited in the file of this patent UNITED STATES PATENTS607,506 Danckwardt July 19, 1898 1,074,988 Steinbuch Oct. 7, 19132,401,821 Gardiner June 11, 1946 2,432,431 MacMullin Dec. 9, 1947FOREIGN PATENTS 740,731 France Nov. 21, 1932

1. APPARATUS FOR ELECTROLYSIS OF A FUSED BATH TO PRODUCE AT THE CATHODEA METAL LIGHTER THAN THE BATH, COMPRISING REFRACTORY WALL STRUCTUREDEFINING A FUSED BATHRECEIVING CELL, A PARTITIONING WALL OF REFRACTORYMATERIAL RISING AND SUPPORTED FROM THE BOTTOM OF THE CELL AND DIVIDINGTHE CELL INTO MAIN AND COLLECTING CHAMBERS, SAID PARTITIONING WALLHAVING OPEN REGIONS THEREIN SPACED BELOW THE TOP OF THE CELL FORCOMMUNICATION BETWEEN THE CHAMBERS, THE AFORESAID WALL STRUCTUREINCLUDING A WALL FOR THE MAIN CHAMBER OPPOSITE THE PARTITIONING WALL,COVER MEANS CLOSING THE MAIN CHAMBER, MEANS FOR EXHAUSTING GAS FROM THEMAIN CHAMBER ABOVE THE FUSED BATH, A PLURALITY OF CATHODES IN PARALLELARRAY IN THE MAIN CHAMBER, EACH CATHODE BEING DISPOSED CROSSWISE OF THEMAIN CHAMBER BETWEEN THE PARTITIONING WALL AND SAID OPPOSITE WALL ANDEACH CATHODE HAVING SUBSTANTIAL EXTENT BOTH VERTICALLY AND CROSSWISE OFTHE MAIN CHAMBER, MEANS EXTENDING LATERALLY THROUGH WALL STRUCTURE OFTHE MAIN CHAMBER OTHER THAN THE PARTITIONING WALL AND SPACED BELOW THETOP OF THE CELL, FOR SUPPORT OF AND ELECTRICAL CONNECTION TO SAIDCATHODES, ANODE MEANS BETWEEN SAID CATHODES IN MUTUALLY FACING RELATIONTHEREWITH, AND MEANS PROVIDING INVERTED TROUGH SURFACES OVER THECATHODES, EXTENDING ACROSS THE MAIN CHAMBER AND THROUGH THE PARTITIONINGWALL, FOR LEADING MOLTEN METAL RELEASED AT THE CATHODES INTO SAIDSUPPLEMENTAL CHAMBER, SAID CATHODES BEING DISPOSED BELOW THE SAID TROUGHSURFACES, AND SAID CELL WALL STRUCTURE HAVING UPPER PARTS AND SAIDPARTITIONING WALL HAVING AN UPPER PORTION, SAID PARTS AND PORTION BEINGABOVE, AND BEING ARRANGED TO HOLD FUSED BATH IN BOTH CHAMBERS TO A LEVELWHOLLY ABOVE SAID INVERTED TROUGH SURFACES, CATHODES, CATHODE SUPPORTMEANS, AND OPEN REGIONS, SAID PARTITIONING WALL WHOLLY SEPARATING THECHAMBERS AT ITS SAID UPPE PORTION.